Twig blight occurs chiefly in sour cherries, especially the bush sour cherry (Prunus cerasus subsp. acida), but in recent years it has also become one of the most important fungus diseases in sweet cherries.
Twig blight occurs chiefly in cherries but also infects apples, apricots, and peaches. Its occurrence is favored by cool, rainy weather.
Pattern of damage
The fungus Monilia laxa triggers an infection via the flowers. Starting from the tips, infected flowers and leaves wilt and desiccate within a few days (Picture 1). The fungus also causes brown rot in the fruit with clumps of gray or light brown spore pustules (Pictures 2 & 3). Infection of twigs causes the formation of cankers and sticky exudate can be found of the twig surface (Pictures 4 & 5).
Infected shoots must be pruned 15 cm back into the healthy wood. Preventive fungicide treatments should be applied when conditions are especially favorable for infection. Two to three applications during the various blooming phases are required. Another preventative measure is to strengthen the vigor of the trees, which then become more resistant to twig blight.